The use of 4-phenylazopyrazolone masking couplers is known in the art. See, for example, U.S. Pat. No. 2,455,170; U.S. Pat. No. 2,428,034; U.S. Pat. No. 2,808,329; U.S. Pat. No. 2,434,272; U.S. Pat. No. 2,704,711; U.S. Pat. No. 2,688,539; U.S. Pat. No. 3,796,574; U.S. Pat. No. 3,476,560; U.S. Pat. No. 4,427,763; EP 213,490; and U.S. Pat. No. 4,777,123 as well as those identified in Research Disclosure December 1989, Section VII, Part G, Publiched by Kenneth Mason Publications, Ltd., Dudley Annex, 12A North Street, Emworth, Hampshire PO10 7DQ, England. These compounds have proven useful since they are yellow colored in unexposed areas and magenta colored in exposed areas. Thus, when in reality the magenta dye formed in a color negative photographic process has a small but significant unwanted absorption in the blue range, this may be balanced somewhat by the relative loss of blue absorption due to conversion of the mask color from yellow to magenta in the exposed areas. Then, an adjustment can be made to the spectral content of the light used to produce the positive from the negative to effectively cancel out the unwanted blue absorption which is now relatively constant across both the exposed and unexposed areas of the negative.
While 4-phenylazopyrazolone masking couplers have been employed as a means of offsetting the unwanted blue absorption of conventional magenta couplers, this means for improving the color rendition has created several deficiencies in the photographic material related to the raw stock keeping of the element. First, the presence of these masking couplers results in increased fogging (non-imagewise silver development) of the photographic emulsion. This is thought to be due to undesired reactions which occur either in the raw stock prior to development or which occur during the development process itself,either of which results in the formation of a phenyldinitrogen species from the masking coupler. This species can then act as a powerful reducing agent for silver emulsions. The result is undesired non-imagewise silver development which manifests itself as fog. Thus, the Dmin (minimum density) of the photographic material is undesirably increased due to the presence of this class of masking coupler. This deficiency is amplified even further in the case of processing using extended development times ("push" processing.)
The second deficiency with the 4-phenylazopyrazolones is their tendency to degrade the photographic properties when bicyclic azole couplers are employed as image couplers. It is believed that the mentioned phenyldinitrogen species is released as a result of decomposition of the azopyrazolone masking coupler and plays a role in the degradation of the bicyclic azole image coupler during long term storage. This unwanted destruction of the image coupler results in the loss of density in the photographic image because less dye will be formed for a given level of exposure. It is undesirable to have a film where the image will vary with the length of raw stock storage time.
Development inhibitor releasing (DIR) couplers are well known for inclusion in photographic layers for purposes of improving sharpness, color etc. but such compounds substantially reduce the contrast of the layer (e.g. by 60%.) Such a loss in contrast can be unacceptable under various circumstances such as in a layer where coupler starvation is desired to achive the desired low level of granularity.
European Patent Application 232,101 discloses a photographic element containing a pyrazolotriazole coupler together with at least 17 mole % of a colored masking coupler which may be of the azopyrazolone type. The presence of the large relative percentage of the masking coupler is said to improve sharpness and grain, but for the reasons aforesaid, a large increase in the fog would be expected as well. There is no suggestion to include a low impact DIR coupler in the magenta layer containing the mask. U.S. Pat. No. 4,777,123 contains similar general disclosure but again does not suggest use of the low impact DIR coupler in the magenta layer.
A problem to be solved is to provide a photographic element and process where an azopyrazolone masking coupler can be used in combination with a bicyclic azole image coupler without incurring degradation upon keeping.